Methods and systems for determining a fuel concentration in engine oil using an intake oxygen sensor

ABSTRACT

Methods and systems are provided for estimating a fuel concentration in engine oil in an engine crankcase. In one example, an engine controller may adjust engine operation such as EGR flow and engine fueling based on the estimated fuel concentration in engine oil. The fuel concentration may be based on an output of an intake oxygen sensor when purge and EGR flow are disabled, engine oil temperature, and fuel composition.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 14/252,679, entitled “METHODS AND SYSTEMS FOR DETERMINING AFUEL CONCENTRATION IN ENGINE OIL USING AN INTAKE OXYGEN SENSOR,” filedon Apr. 14, 2014, the entire contents of which are hereby incorporatedby reference for all purposes.

FIELD

The present description relates generally to a gas constituent sensorincluded in an intake system of an internal combustion engine.

BACKGROUND/SUMMARY

Engine systems may utilize recirculation of exhaust gas from an engineexhaust system to an engine intake system (intake passage), a processreferred to as exhaust gas recirculation (EGR), to reduce regulatedemissions and improve fuel economy. An EGR system may include varioussensors to measure and/or control the EGR. As one example, the EGRsystem may include an intake gas constituent sensor, such as an oxygensensor, which may be employed during non-EGR conditions to determine theoxygen content of fresh intake air. During EGR conditions, the sensormay be used to infer EGR based on a change in oxygen concentration dueto addition of EGR as a diluent. One example of such an intake oxygensensor is shown by Matsubara et al. in U.S. Pat. No. 6,742,379. The EGRsystem may additionally or optionally include an exhaust gas oxygensensor coupled to the exhaust manifold for estimating a combustionair-fuel ratio.

As such, due to the location of the oxygen sensor downstream of a chargeair cooler in the high pressure air induction system, the sensor may besensitive to the presence of fuel vapor and other reductants andoxidants such as oil mist. For example, during boosted engine operation,purge air and/or blow-by gases may be received at a compressor inletlocation. Hydrocarbons ingested from purge air, the positive crankcaseventilation (PCV), and/or rich EGR can consume oxygen on the sensorcatalytic surface and reduce the oxygen concentration detected by thesensor. In some cases, the reductants may also react with the sensingelement of the oxygen sensor. The reduction in oxygen at the sensor maybe incorrectly interpreted as a diluent when using the change in oxygento estimate EGR. Thus, the sensor measurements may be confounded by thevarious sensitivities, the accuracy of the sensor may be reduced, andmeasurement and/or control of EGR may be degraded.

Hydrocarbons in the PCV flow may result from increased fuel in engineoil in a crankcase of the engine. For example, fuel may accumulate inthe engine oil during engine cold start and warm-up conditions. Theaccumulated fuel may then be released as hydrocarbons while the engineis warming up and when the engine oil reaches a steady-state operatingtemperature. Hydrocarbons may affect various engine parameters andcontrols including fuel control and monitoring, engine oil viscosity,and the intake oxygen sensor output. Excessive fuel in the oil maydecrease engine durability.

In one example, the issues described above may be addressed by a methodfor an engine comprising: adjusting engine operation based on a fuelconcentration in engine oil, the fuel concentration based on an outputof an intake oxygen sensor when purge and EGR flow are disabled, engineoil temperature, and fuel composition. A fuel evaporation from theengine oil may also be determined based on the estimated fuelconcentration in engine oil. The fuel concentration in engine oil andthe fuel evaporation rate may provide information as to theconcentration of hydrocarbons in both the engine oil and the intake airwhen the engine is boosted. As a result, an engine controller may adjustengine operation based on the fuel concentration in engine oil and/orthe fuel evaporation rate. In one example, the controller may correct anoutput of the intake oxygen sensor for EGR flow estimation based on thefuel concentration in the engine oil. Subsequently, the controller mayadjust an EGR valve based on the estimated EGR flow. In another example,the controller may adjust fuel injection to the engine based on the fuelevaporation rate. For example, as the fuel evaporation rate increases,the controller may decrease an amount of fuel injection. In yet anotherexample, the controller may use the fuel evaporation rate to predictsubsequent intake oxygen readings from the intake oxygen sensor. If thepredicted intake oxygen reading differs from an actual output of theintake oxygen sensor, the fuel evaporation rate estimation may bedegraded and accurate compensation of the output of the intake oxygensensor for EGR control may not be possible. As a result, the controllermay indicate degradation of the estimation method and trigger a methodto disable EGR flow until the hydrocarbon effect is reduced. In thisway, adjusting engine operation based on the fuel concentration inengine oil and/or the fuel evaporation rate may increase the accuracy ofengine control by providing a way to predict an amount of hydrocarbonsin the intake airflow and subsequently adjust engine fueling and/or EGRflow based on the hydrocarbons in the airflow and engine oil. As aresult, engine longevity may be increased and EGR flow may be deliveredat a requested level.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-2 are schematic diagrams of an engine system.

FIG. 3 is a map depicting the impact of PCV hydrocarbons the oxygenconcentration estimated by an intake oxygen sensor.

FIGS. 4A-4B show a method for disabling EGR flow when a hydrocarbonimpact on an intake oxygen sensor is greater than a threshold.

FIG. 5 shows a method for estimating a fuel concentration in engine oiland a fuel evaporation rate from the engine oil.

FIG. 6 shows a graph of example adjustments to EGR flow based onestimates of an impact of PCV hydrocarbons on an output of an intakeoxygen sensor.

DETAILED DESCRIPTION

The following description relates to systems and methods for estimatingan impact of PCV hydrocarbons on an output of an intake oxygen sensorand estimating a fuel concentration in engine oil. FIGS. 1-2 showexample engines including a low-pressure exhaust gas recirculation (EGR)passage, a PCV system, and an intake oxygen sensor positioned in anintake passage downstream from the inlet of the LP-EGR passage and theinlet of the PCV system (during boosted operation) to the intakepassage. During boosted engine operation, hydrocarbons (HCs) from theengine crankcase may enter the intake passage via PCV flow upstream ofthe intake oxygen sensor. As a result, a decrease in intake oxygenmeasured by the intake oxygen sensor may result from the PCV flow HCsand any additional diluents in the intake airflow (e.g., EGR or purgeflow). This effect is shown at FIG. 3. However, the intake oxygen sensormay assume the decrease in intake oxygen is due to EGR alone and usethis measurement to estimate EGR flow and adjust LP-EGR flow of theengine. As a result, EGR flow may not be adjusted to the desired level(e.g., may be reduced more than necessary). FIGS. 4A-4B show a methodfor estimating the impact of PCV HCs on the intake oxygen sensor output(e.g., PCV noise at the intake oxygen sensor) when purge is disabled. Ifthe impact of PCV HCs on the intake oxygen sensor is greater thanthreshold, an engine controller may disable LP-EGR for a duration untilthe PCV noise is reduced back below the threshold. A source of HCs inthe PCV flow may result from fuel in the engine oil in the crankcase. Asengine oil temperature increases, a greater amount of HCs may bereleased into the air and enter the intake passage via the PCV flow.Example adjustments to EGR based on PCV noise are shown at FIG. 6.Additionally, a method for estimating the fuel concentration in theengine oil and a fuel evaporation rate from the engine oil is shown atFIG. 5. The controller may adjust engine operation responsive to thefuel concentration and fuel evaporation rate. For example, the intakeoxygen sensor output may be adjusted and corrected for PCV flow based onthe estimated fuel concentration in the engine oil. Additionally, flagsindicating a need to disable purge via the method presented at FIG. 4may be generated responsive to the fuel evaporation rate relative tointake oxygen sensor outputs. In this way, EGR adjustments due toinaccurate EGR flow estimates from an intake oxygen sensor impacted byPCV flow HCs may be reduced.

FIG. 1 shows a schematic depiction of an example turbocharged enginesystem 100 including a multi-cylinder internal combustion engine 10 andtwin turbochargers 120 and 130, which may be identical. As onenon-limiting example, engine system 100 can be included as part of apropulsion system for a passenger vehicle. While not depicted herein,other engine configurations such as an engine with a single turbochargermay be used without departing from the scope of this disclosure.

Engine system 100 may be controlled at least partially by a controller12 and by input from a vehicle operator 190 via an input device 192. Inthis example, input device 192 includes an accelerator pedal and a pedalposition sensor 194 for generating a proportional pedal position signalPP. Controller 12 may be a microcomputer including the following: amicroprocessor unit, input/output ports, an electronic storage mediumfor executable programs and calibration values (e.g., a read only memorychip), random access memory, keep alive memory, and a data bus. Thestorage medium read-only memory may be programmed with computer readabledata representing non-transitory instructions executable by themicroprocessor for performing the routines described herein as well asother variants that are anticipated but not specifically listed.Controller 12 may be configured to receive information from a pluralityof sensors 165 and to send control signals to a plurality of actuators175 (various examples of which are described herein). Other actuators,such as a variety of additional valves and throttles, may be coupled tovarious locations in engine system 100. Controller 12 may receive inputdata from the various sensors, process the input data, and trigger theactuators in response to the processed input data based on instructionor code programmed therein corresponding to one or more routines.Example control routines are described herein with regard to FIGS. 4A-6.

Engine system 100 may receive intake air via intake passage 140. Asshown at FIG. 1, intake passage 140 may include an air filter 156 and anair induction system (AIS) throttle 115. The position of AIS throttle115 may be adjusted by the control system via a throttle actuator 117communicatively coupled to controller 12.

At least a portion of the intake air may be directed to a compressor 122of turbocharger 120 via a first branch of the intake passage 140 asindicated at 142 and at least a portion of the intake air may bedirected to a compressor 132 of turbocharger 130 via a second branch ofthe intake passage 140 as indicated at 144. Accordingly, engine system100 includes a low-pressure AIS system (LP AIS) 191 upstream ofcompressors 122 and 132, and a high-pressure AIS system (HP AIS) 193downstream of compressors 122 and 132.

A positive crankcase ventilation (PCV) conduit 198 (e.g., push-sidepipe) may couple a crankcase (not shown) to the second branch 144 of theintake passage such that gases in the crankcase may be vented in acontrolled manner from the crankcase. Further, evaporative emissionsfrom a fuel vapor canister (not shown) may be vented into the intakepassage through a fuel vapor purge conduit 195 coupling the fuel vaporcanister to the second branch 144 of the intake passage.

The first portion of the total intake air can be compressed viacompressor 122 where it may be supplied to intake manifold 160 viaintake air passage 146. Thus, intake passages 142 and 146 form a firstbranch of the engine's air intake system. Similarly, a second portion ofthe total intake air can be compressed via compressor 132 where it maybe supplied to intake manifold 160 via intake air passage 148. Thus,intake passages 144 and 148 form a second branch of the engine's airintake system. As shown at FIG. 1, intake air from intake passages 146and 148 can be recombined via a common intake passage 149 beforereaching intake manifold 160, where the intake air may be provided tothe engine. In some examples, intake manifold 160 may include an intakemanifold pressure sensor 182 for estimating a manifold pressure (MAP)and/or an intake manifold temperature sensor 183 for estimating amanifold air temperature (MCT), each communicating with controller 12.In the depicted example, intake passage 149 also includes a charge aircooler (CAC) 154 and a throttle 158. The position of throttle 158 may beadjusted by the control system via a throttle actuator 157communicatively coupled to controller 12. As shown, throttle 158 may bearranged in intake passage 149 downstream of CAC 154, and may beconfigured to adjust the flow of an intake gas stream entering engine10.

As shown at FIG. 1, a compressor bypass valve (CBV) 152 may be arrangedin CBV passage 150 and a CBV 155 may be arranged in CBV passage 151. Inone example, CBVs 152 and 155 may be electronic pneumatic CBVs (EPCBVs).CBVs 152 and 155 may be controlled to enable release of pressure in theintake system when the engine is boosted. An upstream end of CBV passage150 may be coupled with intake passage 148 downstream of compressor 132,and a downstream end of CBV passage 150 may be coupled with intakepassage 144 upstream of compressor 132. Similarly, an upstream end of aCBV passage 151 may be coupled with intake passage 146 downstream ofcompressor 122, and a downstream end of CBV passage 151 may be coupledwith intake passage 142 upstream of compressor 122. Depending on aposition of each CBV, air compressed by the corresponding compressor maybe recirculated into the intake passage upstream of the compressor(e.g., intake passage 144 for compressor 132 and intake passage 142 forcompressor 122). For example, CBV 152 may open to recirculate compressedair upstream of compressor 132 and/or CBV 155 may open to recirculatecompressed air upstream of compressor 122 to release pressure in theintake system during selected conditions to reduce the effects ofcompressor surge loading. CBVs 155 and 152 may be either actively orpassively controlled by the control system.

As shown, a compressor inlet pressure (CIP) sensor 196 is arranged inthe intake passage 142 and a HP AIS pressure sensor 169 is arranged inintake passage 149. However, in other anticipated embodiments, sensors196 and 169 may be arranged at other locations within the LP AIS and HPAIS, respectively. Among other functions, CIP sensor 196 may be used todetermine a pressure downstream of an EGR valve 121.

Engine 10 may include a plurality of cylinders 14. In the depictedexample, engine 10 includes six cylinders arrange in a V-configuration.Specifically, the six cylinders are arranged on two banks 13 and 15,with each bank including three cylinders. In alternate examples, engine10 can include two or more cylinders such as 3, 4, 5, 8, 10 or morecylinders. These various cylinders can be equally divided and arrangedin alternate configurations, such as V, in-line, boxed, etc. Eachcylinder 14 may be configured with a fuel injector 166. In the depictedexample, fuel injector 166 is a direct in-cylinder injector. However, inother examples, fuel injector 166 can be configured as a port based fuelinjector.

Intake air supplied to each cylinder 14 (herein, also referred to ascombustion chamber 14) via common intake passage 149 may be used forfuel combustion and products of combustion may then be exhausted viabank-specific exhaust passages. In the depicted example, a first bank 13of cylinders of engine 10 can exhaust products of combustion via acommon exhaust passage 17 and a second bank 15 of cylinders can exhaustproducts of combustion via a common exhaust passage 19.

The position of intake and exhaust valves of each cylinder 14 may beregulated via hydraulically actuated lifters coupled to valve pushrods,or via mechanical buckets in which cam lobes are used. In this example,at least the intake valves of each cylinder 14 may be controlled by camactuation using a cam actuation system. Specifically, the intake valvecam actuation system 25 may include one or more cams and may utilizevariable cam timing or lift for intake and/or exhaust valves. Inalternative embodiments, the intake valves may be controlled by electricvalve actuation. Similarly, the exhaust valves may be controlled by camactuation systems or electric valve actuation. In still anotheralternative embodiment, the cams may not be adjustable.

Products of combustion that are exhausted by engine 10 via exhaustpassage 17 can be directed through exhaust turbine 124 of turbocharger120, which in turn can provide mechanical work to compressor 122 viashaft 126 in order to provide compression to the intake air.Alternatively, some or all of the exhaust gases flowing through exhaustpassage 17 can bypass turbine 124 via turbine bypass passage 123 ascontrolled by wastegate 128. The position of wastegate 128 may becontrolled by an actuator (not shown) as directed by controller 12. Asone non-limiting example, controller 12 can adjust the position of thewastegate 128 via pneumatic actuator controlled by a solenoid valve. Forexample, the solenoid valve may receive a signal for facilitating theactuation of wastegate 128 via the pneumatic actuator based on thedifference in air pressures between intake passage 142 arranged upstreamof compressor 122 and intake passage 149 arranged downstream ofcompressor 122. In other examples, other suitable approaches other thana solenoid valve may be used for actuating wastegate 128.

Similarly, products of combustion that are exhausted by engine 10 viaexhaust passage 19 can be directed through exhaust turbine 134 ofturbocharger 130, which in turn can provide mechanical work tocompressor 132 via shaft 136 in order to provide compression to intakeair flowing through the second branch of the engine's intake system.Alternatively, some or all of the exhaust gases flowing through exhaustpassage 19 can bypass turbine 134 via turbine bypass passage 133 ascontrolled by wastegate 138. The position of wastegate 138 may becontrolled by an actuator (not shown) as directed by controller 12. Asone non-limiting example, controller 12 can adjust the position ofwastegate 138 via a solenoid valve controlling a pneumatic actuator. Forexample, the solenoid valve may receive a signal for facilitating theactuation of wastegate 138 via the pneumatic actuator based on thedifference in air pressures between intake passage 144 arranged upstreamof compressor 132 and intake passage 149 arranged downstream ofcompressor 132. In other examples, other suitable approaches other thana solenoid valve may be used for actuating wastegate 138.

In some examples, exhaust turbines 124 and 134 may be configured asvariable geometry turbines, wherein controller 12 may adjust theposition of the turbine impeller blades (or vanes) to vary the level ofenergy that is obtained from the exhaust gas flow and imparted to theirrespective compressor. Alternatively, exhaust turbines 124 and 134 maybe configured as variable nozzle turbines, wherein controller 12 mayadjust the position of the turbine nozzle to vary the level of energythat is obtained from the exhaust gas flow and imparted to theirrespective compressor. For example, the control system can be configuredto independently vary the vane or nozzle position of the exhaust gasturbines 124 and 134 via respective actuators.

Products of combustion exhausted by the cylinders via exhaust passage 19may be directed to the atmosphere via exhaust passage 180 downstream ofturbine 134, while combustion products exhausted via exhaust passage 17may be directed to the atmosphere via exhaust passage 170 downstream ofturbine 124. Exhaust passages 170 and 180 may include one or moreexhaust after-treatment devices, such as a catalyst, and one or moreexhaust gas sensors. For example, as shown at FIG. 1, exhaust passage170 may include an emission control device 129 arranged downstream ofthe turbine 124, and exhaust passage 180 may include an emission controldevice 127 arranged downstream of the turbine 134. Emission controldevices 127 and 129 may be selective catalytic reduction (SCR) devices,three way catalysts (TWC), NO_(x) traps, various other emission controldevices, or combinations thereof. Further, in some embodiments, duringoperation of the engine 10, emission control devices 127 and 129 may beperiodically regenerated by operating at least one cylinder of theengine within a particular air/fuel ratio, for example.

Engine system 100 may further include one or more exhaust gasrecirculation (EGR) systems for recirculating at least a portion ofexhaust gas from the exhaust manifold to the intake manifold. These mayinclude one or more high-pressure EGR systems for proving high pressureEGR (HP EGR) and one or more low-pressure EGR-loops for providing lowpressure EGR (LP EGR). In one example, HP EGR may be provided in theabsence of boost provided by turbochargers 120, 130, while LP EGR may beprovided in the presence of turbocharger boost and/or when exhaust gastemperature is above a threshold. In still other examples, both HP EGRand LP EGR may be provided simultaneously.

In the depicted example, engine system 100 may include a low-pressure(LP) EGR system 108. LP EGR system 108 routes a desired portion ofexhaust gas from exhaust passage 170 to intake passage 142. In thedepicted embodiment, EGR is routed in an EGR passage 197 from downstreamof turbine 124 to intake passage 142 at a mixing point located upstreamof compressor 122. The amount of EGR provided to intake passage 142 maybe varied by the controller 12 via EGR valve 121 coupled in the LP EGRsystem 108. In the example embodiment shown at FIG. 1, LP EGR system 108includes an EGR cooler 113 positioned upstream of EGR valve 121. EGRcooler 113 may reject heat from the recirculated exhaust gas to enginecoolant, for example. The LP EGR system may include a differentialpressure over valve (DPOV) sensor 125. In one example, an EGR flow ratemay be estimated based on the DPOV system which includes the DPOV sensor125 that detects a pressure difference between an upstream region of theEGR valve 121 and a downstream region of EGR valve 121. EGR flow rate(e.g., LP EGR flow rate) determined by the DPOV system may be furtherbased on an EGR temperature detected by an EGR temperature sensor 135located downstream of EGR valve 121 and an area of EGR valve openingdetected by an EGR valve lift sensor 131. In another example, EGR flowrate may be determined based on outputs from an EGR measurement systemthat includes an intake oxygen sensor 168, mass air flow sensor (notshown), manifold absolute pressure (MAP) sensor 182 and manifoldtemperature sensor 183. In some examples, both the EGR measurementsystems (that is, the DPOV system including differential pressure sensor125 and the EGR measurement system including intake oxygen sensor 168)may be used to determine, monitor and adjust EGR flow rate.

In an alternate embodiment, the engine system may include a second LPEGR system (not shown) that routes a desired portion of exhaust gas fromexhaust passage 180 to intake passage 144. In another alternateembodiment, the engine system may include both the LP EGR systems (onerouting exhaust gas from exhaust passage 180 to intake passage 144, andanother routing exhaust gas from exhaust passage 170 to intake passage142) described above.

In the depicted example, the engine system 100 may also include a HP EGRsystem 206. HP EGR system 206 routes a desired portion of exhaust gasfrom common exhaust passage 17, upstream of the turbine 124, to intakemanifold 160, downstream of intake throttle 158. Alternatively, the HPEGR system 206 may be positioned between exhaust passage 17 and theintake passage 193, downstream of the compressor 122 and upstream of theCAC 154. The amount of HP EGR provided to intake manifold 160 may bevaried by the controller 12 via EGR valve 210 coupled in the HP EGRpassage 208. In the example embodiment shown at FIG. 1, HP EGR system206 includes an EGR cooler 212 positioned upstream of EGR valve 210. EGRcooler 212 may reject heat from the recirculated exhaust gas to enginecoolant, for example. The HP EGR system 206 includes a differentialpressure over valve (DPOV) sensor 216. In one example, an EGR flow rate(e.g., HP EGR flow rate) may be estimated based on the DPOV system whichincludes the DPOV sensor 216 that detects a pressure difference betweenan upstream region of EGR valve 210 and a downstream region of EGR valve210. EGR flow rate determined by the DPOV system may be further based onan EGR temperature detected by an EGR temperature sensor 220 locateddownstream of EGR valve 210 and an area of EGR valve opening detected byan EGR valve lift sensor 214. In alternate embodiments, the HP EGRpassage 208 may not include a DPOV system.

Likewise, the engine may include a second high-pressure EGR loop (notshown) for recirculating at least some exhaust gas from the exhaustpassage 19, upstream of the turbine 134, to the intake passage 148,downstream of the compressor 132, or to the intake manifold 160,downstream of intake throttle 158. EGR flow through HP-EGR loops 208 maybe controlled via HP-EGR valve 210.

EGR valve 121 and EGR valve 210 may be configured to adjust an amountand/or rate of exhaust gas diverted through the corresponding EGRpassages to achieve a desired EGR dilution percentage of the intakecharge entering the engine, where an intake charge with a higher EGRdilution percentage includes a higher proportion of recirculated exhaustgas to air than an intake charge with a lower EGR dilution percentage.In addition to the position of the EGR valves, it will be appreciatedthat AIS throttle position of the AIS throttle 115, and other actuatorsmay also affect the EGR dilution percentage of the intake charge. As anexample, AIS throttle position may increase the pressure drop over theLP EGR system, allowing more flow of LP EGR into the intake system. As aresult, this may increase the EGR dilution percentage, whereas less LPEGR flow into the intake system may decrease the EGR dilution percentage(e.g., percentage EGR). Accordingly, EGR dilution of the intake chargemay be controlled via control of one or more of EGR valve position andAIS throttle position among other parameters. Thus, adjusting one ormore of the EGR valves 121 and 210 and/or the AIS throttle 115 mayadjust and EGR flow amount (or rate) and subsequently a percentage EGRin the mass air flow (e.g., air charge entering the intake manifold).

The engine 10 may further include one or more oxygen sensors positionedin the common intake passage 149. As such, the one or more oxygensensors may be referred to as intake oxygen sensors. In the depictedembodiment, an intake oxygen sensor 168 is positioned upstream ofthrottle 158 and downstream of CAC 154. However, in other embodiments,intake oxygen sensor 168 may be arranged at another location alongintake passage 149, such as upstream of the CAC 154. Intake oxygensensor (IAO2) 168 may be any suitable sensor for providing an indicationof the oxygen concentration of the intake charge air (e.g., air flowingthrough the common intake passage 149), such as a linear oxygen sensor,intake UEGO (universal or wide-range exhaust gas oxygen) sensor,two-state oxygen sensor, etc. In one example, the intake oxygen sensors168 may be an intake oxygen sensor including a heated element as themeasuring element. During operation, a pumping current of the intakeoxygen sensor may be indicative of an amount of oxygen in the gas flow.

A pressure sensor 172 may be positioned alongside the oxygen sensor forestimating an intake pressure at which an output of the oxygen sensor isreceived. Since the output of the oxygen sensor is influenced by theintake pressure, a reference oxygen sensor output may be learned at areference intake pressure. In one example, the reference intake pressureis a throttle inlet pressure (TIP) where pressure sensor 172 is a TIPsensor. In alternate examples, the reference intake pressure is amanifold pressure (MAP) as sensed by MAP sensor 182.

Engine system 100 may include various sensors 165, in addition to thosementioned above. As shown in FIG. 1, common intake passage 149 mayinclude a throttle inlet temperature sensor 173 for estimating athrottle air temperature (TCT). Further, while not depicted herein, eachof intake passages 142 and 144 may include a mass air flow sensor oralternatively the mass air flow sensor can be located in common duct140.

Humidity sensor 189 may be included in only one of the parallel intakepassages. As shown in FIG. 1, the humidity sensor 189 is positioned inthe intake passage 142 (e.g., non PCV and non-purge bank of the intakepassage), upstream of the CAC 154 and an outlet of the LP EGR passage197 into the intake passage 142 (e.g., junction between the LP EGRpassage 197 and the intake passage 142 where LP EGR enters the intakepassage 142). Humidity sensor 189 may be configured to estimate arelative humidity of the intake air. In one embodiment, humidity sensor189 is a UEGO sensor configured to estimate the relative humidity of theintake air based on the output of the sensor at one or more voltages.Since purge air and PCV air can confound the results of the humiditysensor, the purge port and PCV port are positioned in a distinct intakepassage from the humidity sensor.

Intake oxygen sensor 168 may be used for estimating an intake oxygenconcentration and inferring an amount of EGR flow through the enginebased on a change in the intake oxygen concentration upon opening of theEGR valve 121. Specifically, a change in the output of the sensor uponopening the EGR valve 121 is compared to a reference point where thesensor is operating with no EGR (the zero point). Based on the change(e.g., decrease) in oxygen amount from the time of operating with noEGR, an EGR flow currently provided to the engine can be calculated. Forexample, upon applying a reference voltage (Vs) to the sensor, a pumpingcurrent (Ip) is output by the sensor. The change in oxygen concentrationmay be proportional to the change in pumping current (delta Ip) outputby the sensor in the presence of EGR relative to sensor output in theabsence of EGR (the zero point). Based on a deviation of the estimatedEGR flow from the expected (or target) EGR flow, further EGR control maybe performed.

A zero point estimation of the intake oxygen sensor 168 may be performedduring idle conditions where intake pressure fluctuations are minimaland when no PCV or purge air is ingested into the low pressure inductionsystem. In addition, the idle adaptation may be performed periodically,such as at every first idle following an engine start, to compensate forthe effect of sensor aging and part-to-part variability on the sensoroutput.

A zero point estimation of the intake oxygen sensor may alternatively beperformed during engine non-fueling conditions, such as during adeceleration fuel shut off (DFSO). By performing the adaptation duringDFSO conditions, in addition to reduced noise factors such as thoseachieved during idle adaptation, sensor reading variations due to EGRvalve leakage can be reduced.

Now turning to FIG. 2, another example embodiment 200 of the engine ofFIG. 1 is shown. As such, components previously introduced in FIG. 1 arenumbered similarly and not re-introduced here for reasons of brevity.

Embodiment 200 shows a fuel tank 218 configured to deliver fuel toengine fuel injectors. A fuel pump (not shown) immersed in fuel tank 218may be configured to pressurize fuel delivered to the injectors ofengine 10, such as to injector 166. Fuel may be pumped into the fueltank from an external source through a refueling door (not shown). Fueltank 218 may hold a plurality of fuel blends, including fuel with arange of alcohol concentrations, such as various gasoline-ethanolblends, including E10, E85, gasoline, etc., and combinations thereof. Afuel level sensor 219 located in fuel tank 218 may provide an indicationof the fuel level to controller 12. As depicted, fuel level sensor 219may comprise a float connected to a variable resistor. Alternatively,other types of fuel level sensors may be used. One or more other sensorsmay be coupled to fuel tank 218 such as a fuel tank pressure transducer220 for estimating a fuel tank pressure.

Vapors generated in fuel tank 218 may be routed to fuel vapor canister22, via conduit 31, before being purged to engine intake 23. These mayinclude, for example, diurnal and refueling fuel tank vapors. Thecanister may be filled with an appropriate adsorbent, such as activatedcharcoal, for temporarily trapping fuel vapors (including vaporizedhydrocarbons) generated in the fuel tank. Then, during a later engineoperation, when purge conditions are met, such as when the canister issaturated, the fuel vapors may be purged from the canister into theengine intake by opening canister purge valve (CPV) 112 and canistervent valve 114.

Canister 22 includes a vent 27 for routing gases out of the canister 22to the atmosphere when storing, or trapping, fuel vapors from fuel tank218. Vent 27 may also allow fresh air to be drawn into fuel vaporcanister 22 when purging stored fuel vapors to engine intake 23 viapurge lines 90 or 92 (depending on boost level) and purge valve 112.While this example shows vent 27 communicating with fresh, unheated air,various modifications may also be used. Vent 27 may include a canistervent valve 114 to adjust a flow of air and vapors between canister 22and the atmosphere. The vent valve may be opened during fuel vaporstoring operations (for example, during fuel tank refueling and whilethe engine is not running) so that air, stripped of fuel vapor afterhaving passed through the canister, can be pushed out to the atmosphere.Likewise, during purging operations (for example, during canisterregeneration and while the engine is running), the vent valve may beopened to allow a flow of fresh air to strip the fuel vapors stored inthe canister.

Fuel vapors released from canister 22, for example during a purgingoperation, may be directed into engine intake manifold 160 via purgeline 28. The flow of vapors along purge line 28 may be regulated bycanister purge valve 112, coupled between the fuel vapor canister andthe engine intake. The quantity and rate of vapors released by thecanister purge valve 112 may be determined by the duty cycle of anassociated canister purge valve solenoid (not shown). As such, the dutycycle of the canister purge valve solenoid may be determined by thevehicle's powertrain control module (PCM), such as controller 12,responsive to engine operating conditions, including, for example,engine speed-load conditions, an air-fuel ratio, a canister load, etc.The duty cycle may include a frequency (e.g., rate) of opening andclosing the canister purge valve 112.

An optional canister check valve (not shown) may be included in purgeline 28 to prevent intake manifold pressure from flowing gases in theopposite direction of the purge flow. As such, the check valve may benecessary if the canister purge valve control is not accurately timed orthe canister purge valve itself can be forced open by a high intakemanifold pressure. An estimate of the manifold absolute pressure (MAP)may be obtained from MAP sensor 182 coupled to intake manifold 160 andcommunicated with controller 12. Alternatively, MAP may be inferred fromalternate engine operating conditions, such as mass air flow (MAF), asmeasured by a MAF sensor coupled to the intake manifold.

Purge hydrocarbons may be directed to intake manifold 160 via either aboost path 92 or a vacuum path 90 based on engine operating conditions.Specifically, during conditions when turbocharger 120 is operated toprovide a boosted aircharge to the intake manifold, the elevatedpressure in the intake manifold causes one-way valve 94 in the vacuumpath 90 to close while opening one-way valve 96 in the boost path 92. Asa result, purge air is directed into the air intake passage 140,downstream of air filter 156 and upstream of charge air cooler 154 viathe boost path 92. Herein, the purge air is introduced upstream ofintake oxygen sensor 168. In some embodiments, as depicted, a venturi 98may be positioned in the boost path such that the purge air is directedto the intake upon passing through the venturi and passage 99. Thisallows the flow of purge air to be advantageously harnessed for vacuumgeneration.

During conditions when engine 10 is operated without boost, elevatedvacuum in the intake manifold causes one-way valve 94 in the vacuum pathto open while closing one-way valve 96 in the boost path. As a result,purge air is directed into the intake manifold 160, downstream ofthrottle 158 via the vacuum path 90. Herein, the purge air is introduceddownstream of intake oxygen sensor 168.

PCV hydrocarbons may also be directed to intake manifold 160 via eithera boost side PCV hose 252 or a vacuum side PCV hose 254 based on engineoperating conditions.

Specifically, blow-by gases from engine cylinders 14 flow past thepiston rings and enter crankcase 255. During conditions whenturbocharger 120 is operated to provide a boosted aircharge to theintake manifold, the elevated pressure in the intake manifold causesone-way valve 256 in vacuum side PCV hose 254 to close. As a result,during boosted engine operation, PCV gases flow in a first direction(arrow 264) and are received in the engine intake upstream of the intakeoxygen sensor 168. Specifically, PCV air is directed into the air intakepassage 140, downstream of air filter 156 and upstream of charge aircooler 154 via boost side PCV hose 252. The PCV flow may be directed tothe intake passage upon passage through a boost side oil separator 260.The boost side oil separator may be integrated into the cam cover or maybe an external component. Thus, during boosted conditions, the PCV gasesare introduced upstream of intake oxygen sensor 168 and therefore doaffect the output of oxygen sensor 168. The boosted conditions mayinclude intake manifold pressure above ambient pressure.

In comparison, during conditions when engine 10 is operated withoutboost, elevated vacuum in the intake manifold causes one-way valve 256in the vacuum side PCV hose 254 to open. As a result, during non-boostedengine operating, PCV gases flow in a second direction (arrow 262)different from the first direction and are received in the engine intakedownstream of the intake oxygen sensor 168. In the depicted example, thesecond direction of PCV flow during non-boosted engine operation isopposite of the first direction of PCV flow during boosted engineoperation (compare arrows 262 and 264). Specifically, during non-boostedoperation, PCV air is directed into the intake manifold 160, directly,downstream of throttle 158 via the vacuum side PCV hose 254. The PCVflow may be directed to the intake manifold 160 upon passage through avacuum side oil separator 258. Herein, the PCV air is introduceddownstream of intake oxygen sensor 168, and therefore does not affectthe output of oxygen sensor 168. Thus, due to the specific engineconfiguration, during boosted engine operation, PCV and purge airhydrocarbons are ingested into the engine intake manifold upstream ofthe intake oxygen sensor 168 and are ingested into the engine intakemanifold downstream of the intake oxygen sensor during non-boostedconditions.

As previously discussed, the intake air oxygen sensor 168 can be used tomeasure the amount of EGR in the intake aircharge as a function of theamount of change in oxygen content due to the addition of EGR as adiluent. Thus, as more EGR is introduced, the sensor may output areading or pumping current corresponding to a lower oxygenconcentration. During the estimation, a nominal reference voltage (e.g.,at 450 mV), or Nernst voltage, is applied to the sensor and an output(e.g., a pumping current output by the sensor upon application of thelower reference voltage) is noted. Based on the output of the sensorrelative to a zero point of the sensor (that is, sensor output at no EGRconditions), a change in oxygen concentration is learned, and an intakedilution with EGR is inferred.

However, if the EGR estimation is performed during conditions whenpurging and/or crankcase ventilation is enabled (e.g., PCV flow isenabled), an output of the sensor is corrupted. Said another way, PCVand/or fuel vapor purge flow may cause an error in the output of theintake oxygen sensor. As such, purge air and/or positive crankcaseventilation hydrocarbons (e.g., PCV flow) may be ingested during boostedengine operating conditions along boost path 92 and boost side PCV hose252 when the purge valve 112 is open and/or the PCV valve 256 is closed.The sensor output may be corrupted primarily due to the ingestedhydrocarbons reacting with ambient oxygen at the sensing element of theintake sensor. This reduces the (local) oxygen concentration read by thesensor. Since the output of the sensor and the change in oxygenconcentration is used to infer an EGR dilution of intake aircharge, thereduced oxygen concentration read by the intake oxygen sensor in thepresence of purge air and/or PCV may be incorrectly interpreted asadditional diluent. This impacts the EGR estimation and the subsequentEGR control. Specifically, EGR may be over-estimated.

FIG. 3 depicts this variation in the reading of the intake sensor.Specifically, map 300 depicts an oxygen concentration estimated by anintake manifold oxygen sensor along the y-axis and a PCV hydrocarbon(HC) content along the x-axis at a given EGR level. As the amount of PCVHCs ingested into the engine intake manifold increases, such as when PCVis enabled or flowing from the push-side pipe (e.g., conduit 198) duringboosted conditions, the hydrocarbons react with oxygen at the sensingelement of the intake oxygen sensor. The oxygen is consumed and waterand carbon dioxide is released. As a result, the estimated oxygenconcentration is reduced, even though an amount of EGR flow may remainconstant. This reduction in oxygen concentration estimated by the oxygensensor may be inferred as an increased dilution (or replacement ofoxygen with EGR). Thus, the controller may infer that there is a largeramount of EGR flow available than actually is present. If not correctedfor the hydrocarbon effect, a controller may decrease EGR flow inresponse to an incorrect indication of higher EGR dilution, degradingEGR control. For example, during purge and/or PCV flow conditionsresulting in EGR over-estimation, the controller may decrease an openingof the EGR valve in response to a higher EGR estimate (based on a lowerintake oxygen measurement from the intake oxygen sensor). However,actual EGR may be lower than the estimated level. Thus, EGR flow may beincorrectly reduced instead of maintained or increased. This may, inturn, result in increased engine emissions and degraded engineperformance.

In one example, adjusting an intake oxygen measurement based on PCV flowmay increase the accuracy of EGR flow estimates. Specifically, undercertain engine operating conditions, an engine controller (such ascontroller 12 shown in FIG. 1) may determine a PCV flow contribution tothe intake oxygen concentration measured at an intake oxygen sensor(such as the intake oxygen sensor 168 shown in FIGS. 1-2). If the PCVflow effect on intake oxygen under boost conditions is known, thecontroller may use this to correct the measured intake oxygen used toestimate EGR flow. As such, the EGR estimate may be corrected based onPCV flow.

For example, a blow-by map may be stored within a memory of thecontroller. The blow-by map may include an expected blow-by (e.g.,expected amount of combustion chamber gases (predominantly inert)leaking through piston rings and/or compressor/turbine seals and flowingvia PCV push-side pipe (e.g., conduit 198) to the intake and intakeoxygen sensor) for current engine operating conditions. The blow-by mapmay be pre-determined during engine testing and may include an expectedamount of blow-by for a current manifold pressure (MAP) and enginespeed. In this way, the blow-by map may be in a form of a look-up tableand may be used as a baseline for PCV push side flow (e.g., flow fromPCV and to intake upstream of the oxygen sensor) with no hydrocarbons.Any measured hydrocarbons in excess of this amount may indicateexcessive evaporation of crankcase fuel and hence high levels of noiseto the IAO2 sensor reading.

One source of the hydrocarbons (HCs) in PCV flow may be from fuelaccumulation in the engine oil in the crankcase of the engine. Duringengine cold start and warm-up conditions fuel may accumulate in theengine oil. Then, when the engine oil is warming up and/or after theengine oil has warmed up to a steady-state operating temperature, theaccumulated fuel may be released as HCs into the air and PCV flow. Thereleased HCs may affect fuel control and engine oil viscosity, therebydecreasing engine durability. As discussed above, when the engine isboosted, PCV flow may enter the engine intake upstream of the intakeoxygen sensor. As a result, the HCs in the PCV may also affect theoutput of the intake oxygen sensor, thereby decreasing the accuracy ofEGR flow estimation from the intake oxygen sensor output. In this way,the HCs in the intake airflow upstream of the intake oxygen sensor mayresult in measurement noise at the intake oxygen sensor.

By determining a fuel concentration in the engine oil, a hydrocarbonconcentration in the intake airflow upstream of the intake oxygensensor, and/or a fuel (e.g., hydrocarbon) evaporation rate from theengine oil, the effect of released HCs on engine fueling, the intakeoxygen sensor, and consequently EGR flow estimates may be learned. Thislearned data may then be used to adjust engine operation includingengine fueling, EGR flow rate, purge control, oil quality or viscositymonitor, etc. An instantaneous hydrocarbon concentration in the engineoil and fuel evaporation rate from the engine oil may be estimated basedon one or more of engine oil temperature (EOT), an engine boostingcondition, fuel composition (e.g., ethanol content of fuel used in theengine), compressor inlet pressure, crankcase pressure, and intakeoxygen concentration measured from the intake oxygen sensor (e.g., suchas the intake oxygen sensor 168 shown in FIGS. 1-2), or a model of anyof or any combination of the above measurements. Specifically, themethod of determining the instantaneous hydrocarbon concentration inengine oil and/or the fuel evaporation rate may include obtaining anintake oxygen sensor reading when EGR flow and purge flow are disabledand when the engine is boosted. As a result, the decrease in oxygenconcentration measured at the intake oxygen sensor may be due to HCsfrom PCV flow alone and not due to additional diluents such as EGR flowand purge flow HCs. Further, when the engine is boosted, HCs from thecrankcase are directed to the intake passage upstream of the intakeoxygen sensor. The intake oxygen sensor may then be divided by anestimated vapor pressure to determine the instantaneous concentration ofHCs in the engine oil. The vapor pressure may be based on the EOT andthe fuel composition (e.g., the amount of heavy vs. light ends in thefuel). The fuel evaporation rate may then be determined based on a HCconcentration gradient between the liquid and gaseous phases. The HCconcentration in the liquid phase is the concentration of HCs in theengine oil and the HC concentration in the gaseous phased isapproximated by the intake oxygen measurement of the intake oxygensensor. The instantaneous HC concentration in engine oil and the fuelevaporation rate may be stored in a memory of the controller and thenupdated as subsequent intake oxygen sensor measurements are obtained.

In one example, the controller may use the determined fuel evaporationrate to adjust fuel injection to the engine. For example, as theestimated fuel evaporation rate increases, the controller may decreasefueling to the engine. In this way, the controller may adjust fuelinjection based on the fuel evaporation rate estimates. Additionally,the controller may use the determined instantaneous HC concentration toadjust the intake oxygen sensor output (e.g., correct the intake oxygensensor output for PCV HCs) and then estimate EGR flow based on theadjusted intake oxygen sensor output. The controller may then adjust anEGR valve based on the estimated EGR flow, thereby resulting in EGRcontrol with increased accuracy. Methods for determining fuelevaporation rate, instantaneous hydrocarbon concentration in the engineoil, and adjusting engine operation based these values are discussedfurther below with reference to FIGS. 4A-5.

Additionally, when HCs exiting the crankcase through the PCV flow affectthe intake oxygen sensor output, the controller may disable EGR (e.g.,close an EGR valve) until the PCV impact on measured intake oxygenreduces below a threshold. In this way, EGR flow adjustments based onintake oxygen measurements reflecting a decrease in intake oxygen due toEGR and PCV HCs may be reduced. For example, if the engine systemincludes a LP EGR system, the controller may disable LP EGR flow whenEGR flow estimates based on intake oxygen sensor output may have reducedaccuracy due to PCV flow HCs. More specifically, the controller maydisable LP EGR flow when the PCV HC impact on the intake oxygen sensoris greater than a threshold. The threshold may be based on a PCV HCamount that results in an EGR flow estimate different than actual EGRflow by an amount that may result in degraded EGR control. In oneexample, the PCV HC impact on the sensor may be determined based on adifference between the intake oxygen sensor output and estimated blow-by(determined from blow-by map) when both purge and EGR (LP EGR) aredisabled (e.g., turned off). For example, the intake oxygen sensoroutput may be a change in intake oxygen (from a baseline or zero pointvalue) due to HCs in the intake airflow. A difference between thisintake oxygen sensor output and the expected blow-by indicate a largeramount of HCs than expected in the intake airflow. The increased amountof HCs may be from PCV and may result in degraded EGR estimates and EGRcontrol. Thus, if the difference between the intake oxygen sensor outputand the expected blow-by is greater than a threshold, the controller maydisable EGR until the PCV HC impact decreases back below the threshold.

In another example, the PCV HC impact on the intake oxygen sensor may bedetermined based on a difference between a DPOV sensor reading and theintake oxygen sensor reading when purge is disabled and when LP EGR isnot disabled (e.g., EGR is flowing). As described above, the DPOV sensormay be used to determine EGR flow. A first EGR flow estimate based onthe DPOV sensor output may then be compared to a second EGR flowestimate based on the intake oxygen sensor output. If the differencebetween the DPOV sensor estimate and the intake oxygen sensor estimatefor EGR is greater than a threshold, HCs from PCV may be affecting theoxygen reading and the controller may disable EGR until the PCV HCimpact decreases back below the threshold. The controller may determinethe PCV HC impact on the intake oxygen sensor when the engine isboosted, for example, only when the engine is boosted. Additionally, thecontroller may disable EGR based on the determined PCV HC impact onlywhen the engine is boosted since the intake oxygen sensor reading is notaffected by PCV HCs during non-boosted engine operation when the PCV HCsenter the intake passage downstream of the intake oxygen sensor.

In yet another example, the instantaneous HC concentration and/or thefuel evaporation rate determined by the method described above andpresented at FIG. 5 may be used in determining the PCV HC impact on theintake oxygen sensor. If the PCV impact on the intake oxygen sensorcannot be determined or compensated for (e.g., cannot determine theinstantaneous HC concentration in engine oil and/or the evaporationrate), the controller may set a diagnostic code (e.g., flag). Thisdiagnostic code may then be used by the controller to trigger disablingthe EGR flow. The PCV flow impact may not be able to be determined orcompensated for during conditions when the fuel evaporation model isdegraded. For example, the fuel evaporation rate may be used to predictsubsequent intake oxygen measurements from the intake oxygen sensor. Ifa predicted intake oxygen sensor output based on the estimated fuelevaporation rate differs from an actual intake oxygen sensor output, theestimated evaporation rate may not be accurate. As a result, thecontroller may set a flag or diagnostic code indicating that theestimated HC concentration values used for intake oxygen sensor outputcompensation are degraded. As a result, the controller may set a flagand/or command that EGR be disabled for a duration until the accuracy ofthe fuel evaporation rate model increases back above a threshold.

In this way, when HCs are impacting intake oxygen sensor measurements,thereby resulting in inaccurate EGR flow estimates, the controller maydisable EGR flow until the PCV HC impact decreases below a setthreshold. As a result, EGR flow may only be enabled and adjusted whenthe PCV flow effect on the intake oxygen sensor may be compensated for,thereby resulting in EGR flow estimates of increased accuracy. Further,by estimating the evaporation rate and/or the instantaneous HCconcentration in the intake air upstream from the intake oxygen sensor,the controller may improve the accuracy of fuel injection and EGR flowadjustments, thereby increasing engine efficiency.

The systems of FIGS. 1-2 described above provide for an engine system,comprising: an intake manifold, a crankcase coupled to the intakemanifold via a PCV valve, a turbocharger with an intake compressor, anexhaust turbine, and a charge air cooler, an intake throttle coupled tothe intake manifold downstream of the charge air cooler, and a canisterconfigured to receive fuel vapors from a fuel tank, the canister coupledto the intake manifold via a purge valve. The system further comprises alow-pressure exhaust gas recirculation (EGR) passage coupled between anexhaust passage downstream of the exhaust turbine and an intake passageupstream of the intake compressor, the low-pressure EGR passageincluding a low-pressure EGR valve and low-pressure DPOV sensor formeasuring low-pressure EGR flow. The system further comprises an intakeoxygen sensor coupled to the intake manifold downstream of the chargeair cooler and upstream of the intake throttle and a controller withcomputer readable instructions for disabling EGR flow responsive to adifference between an output of the intake oxygen sensor and an outputof the DPOV sensor increasing above a first threshold when EGR isflowing and purge flow is disabled. The computer readable instructionsfurther include instructions for maintaining EGR flow disabledresponsive to a difference between the output of the intake oxygensensor and expected blow-by increasing above a second threshold when EGRis not flowing and purge flow is disabled. The instructions also includeinstructions for maintaining the EGR flow disabled until the differencebetween the output of the intake oxygen sensor and expected blow-bydecreases back below the second threshold.

As another embodiment, the computer readable instructions includeinstructions for: adjusting the low-pressure EGR valve based on anestimated fuel concentration in engine oil and an output of the intakeoxygen sensor, the estimated fuel concentration in engine oil based onthe output of the intake oxygen sensor when purge and EGR flow aredisabled, engine oil temperature, and fuel composition. The computerreadable instructions further include instructions for adjusting fuelinjection to the injection based on an evaporation rate of fuel from thecrankcase, the evaporation rate based on a concentration gradientbetween the estimated fuel concentration in engine oil and the output ofthe intake oxygen sensor. In another example, the computer readableinstructions further include closing the low-pressure EGR valve in orderto disable EGR flow responsive to a difference between a predictedoutput of the intake oxygen sensor and an actual output of the intakeoxygen sensor being greater than a threshold amount, the predictedoutput of the intake oxygen sensor based on the evaporation rate. Thethreshold amount may be an amount indicative of increased hydrocarbonsin the intake airflow upstream of the intake airflow. As a result,compensation for the PCV hydrocarbons may not be possible for EGR flowestimation.

Turning now to FIGS. 4A-4B, a method 400 is shown for disabling EGR flowwhen a hydrocarbon impact on an intake oxygen sensor is greater than athreshold. As described above, an increase in HC impact on the intakeoxygen sensor (IAO2) may be due to PCV flow HCs during boosted engineoperation. As shown in FIGS. 1-2, the IAO2 may be positioned in anintake passage, downstream of a compressor, an inlet of a LP EGR passageinto the intake passage, and a push-side PCV passage (e.g., boost path92 shown in FIG. 2). The LP EGR passage may include a DPOV sensorcoupled to the LP EGR valve. Instructions for carrying out method 400may be stored in a memory of an engine controller such as controller 12shown in FIGS. 1-2. Further, method 400 may be executed by thecontroller.

Method 400 begins by estimating and/or measuring engine operatingconditions at 402. Engine operating conditions may include an engineboost condition (e.g., boost level and boost on/off), EGR flow, MAP,engine speed, engine load, engine oil temperature (EOT), barometricpressure, humidity, crankcase pressure, etc. At 404, the method includesdetermining if the engine is boosted. If the engine is not boosted, themethod continues to 406 to adjust EGR flow based on the IAO2 output andnot estimate PCV (or HC) noise at the IAO2. The impact of PCV HCs on theIAO2 output may be referred to herein as PCV noise at the IAO2. Asdiscussed above, when the engine is unboosted, PCV flow enters theengine intake downstream of the IAO2, thereby having no effect on theintake oxygen measured by the IAO2. However, if the engine is boosted,PCV HCs may enter the intake airflow upstream of the IAO2, therebyimpacting the IAO2.

If the engine is boosted, the method continues on to 408 to determine ifpurge flow is off. For example, if a purge valve is closed and no purgeis flowing to the intake passage, purge flow is disabled (e.g., off). Asdiscussed above, in order to determine the impact of PCV HCs on theIAO2, purge must be disabled. Thus, if purge is not disabled, the methodcontinues to 410 to determine if it is time to disable purge. Theroutine for determining the HC impact on the IAO2 may be run at a setfrequency. For example, the IAO2 output relative to estimated blow-by ora DPOV sensor output (based on whether EGR is flowing or not, asdescribed further below) may be checked at a set frequency in order todetermine the PCV noise at the IAO2. If it is not time to disable purgefor determining the PCV HC impact on the IAO2, the controller does notdisable purge at 411. The method may return and wait until it is time todisable purge, as defined by the set checking frequency. In one example,the set checking frequency may be based on EOT. Specifically, if theengine is warming up (e.g., EOT is below a steady-state operatingtemperature), the checking frequency may be set to a first level basedon the increasing EOT. For example, for each threshold increase in EOT(e.g., 5° C.) the controller may disable purge and determine the PCV HCimpact on the IAO2. Once the EOT reaches steady-state such that the EOTis relatively constant, the controller may disable purge and determinethe PCV noise less frequently. For example, purge may only be disabledonce for determining PCV noise when the EOT is at steady-state. Then,following steady-state when the EOT begins to increase or decrease, thechecking frequency may return to the first level based on the change inEOT.

Conversely at 410, if it is time to estimate PCV noise at the IAO2, thecontroller may disable purge at 412. Disabling purge may include closinga purge valve (e.g., CPV valve 112 shown in FIG. 2). At 414, the methodincludes determining if EGR is disabled (e.g., turned off). EGR may bedisabled if the EGR valve is closed. As discussed above, the EGR may beLP EGR including a LP EGR passage with an inlet positioned upstream ofthe compressor and IAO2 in the intake passage. If EGR is disabled, themethod continues on to 417 to obtain a measurement from the IAO2. Themethod may then continue on to 418 to determine the HC concentration inengine oil and/or a fuel evaporation rate from the engine oil based onthe IAO2 output. The method for determining the HC concentration andfuel evaporation rate is shown at FIG. 5, described further below. Inalternate embodiments, method 400 may not include determining the HCconcentration in the oil and the fuel evaporation rate.

At 420, the method includes determining if a difference between the IAO2output and an estimated blow-by is greater than a first threshold and/orif a flag has been set based on the fuel evaporation rate (as determinedby the method presented at FIG. 5). For example, the IAO2 output may bea change in intake oxygen from a reference point due to diluents in theairflow. Since EGR and purge are both disabled, the decrease in intakeoxygen measured by the IAO2 may be due to PCV HCs alone and not due toEGR and purge flow. As discussed above, the expected blow-by may be anexpected amount of HCs in the intake airflow from PCV flow at thecurrent engine operating conditions. Determining the expected blow-bymay include looking up the expected blow-by in a look-up table or mapstored in the memory of the controller. The expected blow-by may be afunction of the current MAP and engine speed. Alternatively, the blow-bymap may be determined by using the intake oxygen sensor measurementafter an oil change when the fuel in the oil is negligible. The firstthreshold may be based on an amount of HCs indicating increased PCV HCsat the IAO2. The increased PCV HCs may be indicative of increased PCVnoise resulting in EGR flow estimates of reduced accuracy. Additionally,the flag based on the fuel evaporation rate may be indicative of morePCV HCs than predicted by the fuel evaporation rate in the intakeairflow. As a result, IAO2 compensation based on the estimated HCconcentration in the engine oil (and the fuel evaporation rate) may notbe accurate and may lead to EGR flow estimates of reduce accuracy. Thus,if the diagnostic flag indicating degraded fuel evaporation rateestimation is set and/or the difference between the IAO2 output and theexpected blow-by is greater than the first threshold, the controller maydisable EGR at 430 (shown in FIG. 4B). The controller may disable EGRuntil the PCV HC impact on the IAO2 decreases back below the threshold.Thus, the method at 430 may also include re-checking the PCV noise at asecond frequency. The second frequency may be different than the setchecking frequency described above at 410. For example, the secondfrequency may be a set amount of time or duration between determiningthe PCV noise at the IAO2. In some examples, the second frequency may begreater than the set checking frequency (and the first frequency asdescribed further below with reference to 424) such that the PCV noiseis checked more frequently when EGR has been disabled due to the PCV HCimpact greater than the threshold. If the impact of PCV flow HCs on theIAO2 output is less than or equal to the threshold (e.g., the firstthreshold) during the re-checking at 432, the method continues to 434 tore-enable EGR. The method at 434 then returns to checking for PCV noiseat a first frequency based on EOT.

Returning to 420, if neither a flag is set based on the fuel evaporationrate nor the difference between the IAO2 output and the expected blow-byis greater than the first threshold, the method continues on to 424 tonot disable EGR. The method at 424 also includes re-x′ checking PCVnoise at the first frequency based on EOT, the first frequency lowerthan the second frequency such that the PCV noise is checked less oftenat the first frequency (e.g., a duration between subsequent PCV noisechecks is longer at the first frequency when EGR is not disabled than atthe second frequency when EGR is disabled).

Returning to 414, if EGR is not disabled (e.g., LP EGR is flowing and aLP EGR valve is at least partially open), the method continues on to 415to determine if the engine includes a DPOV sensor. In some embodiments,the method at 415 may also include determining if the DPOV sensor iscurrently functioning properly. If a DPOV sensor is not present in theengine system (e.g., a DPOV sensor is not present for measuring LP EGRand/or HP EGR) or if the DPOV sensor is degraded, the method proceeds to416 to disable EGR and continues on to 417 to obtain a measurement fromthe IAO2. The method then proceeds to 418 to determine the HCconcentration in the oil and the evaporation rate from the IAO2 outputand expected blow-by and not the DPOV sensor output. In this way, if noDPOV sensor is present, the method may turn off EGR in order todetermine the impact of HCs on the IAO2 (e.g., determine the noise atthe IAO2).

If, at 415, a DPOV sensor is included in the engine, the method maycontinue to 426 to obtain a measurement from the IAO2 and a measurementfrom the DPOV sensor in the LP EGR passage. As a result of the enginesystem including a DPOV sensor, EGR does not need to be turned off inorder to determine the impact of HCs on the IAO2. Thus, determining PCVnoise at the IAO2 may be performed less intrusively when a DPOV sensoris present and may be used to estimate EGR flow for comparison with theIAO2 output.

At 428, the method includes determining if an absolute value of adifference between the IAO2 output and the DPOV sensor output is greaterthan a second threshold. The second threshold may be indicative of anincreased amount of HCs from PCV flow in the intake airflow which mayresult in a lower intake oxygen sensor measurement, thereby resulting inan EGR flow measurement of reduced accuracy. This may result inincorrect EGR flow adjustment, thereby degrading engine control. If thedifference between the IAO2 output and the DPOV sensor output is notgreater than the second threshold, the method continues on to 424 to notdisable EGR and continue checking for PCV noise at the IAO2 at the firstfrequency based on EOT. However, if the difference between the IAO2output and the DPOV sensor output is greater than the second threshold,the method continues on to 420 (shown in FIG. 4B) to disable EGR andre-check for PCV noise at the second frequency based on a set timeduration. The method than continues on to 432 and 434 as describedabove. For example, after disabling EGR the method at 432 includesdetermining if the impact of PCV flow HCs on the IAO2 output is lessthan or equal to the threshold. The impact of PCV flow HCs may bedetermined from the difference between the IAO2 output and estimatedblow-by and not the difference between the IAO2 output and the DPOVsensor output since EGR is disabled at 432.

In this way, a method for an engine comprises disabling EGR flowresponsive to an impact of PCV flow hydrocarbons on an output of anintake oxygen sensor increasing above a threshold when purge flow isdisabled, the impact of PCV flow hydrocarbons based a difference betweenthe output of the intake oxygen sensor and an output of a DPOV sensorwhen EGR is flowing. In one example, the impact of PCV flow hydrocarbonsis based on a difference between the output of the intake oxygen sensorand expected blow-by when EGR is not flowing. The expected blow-by isbased on a pre-determined blow-by amount for a current manifold pressureand engine speed. For example, the expected blow-by may be stored withina look-up table in a memory of a controller of the engine. Inputs to thelook-up table may include the current manifold pressure and enginespeed. In alternate embodiments, the inputs to the look-up table may bealternative or additional engine operating conditions such as boostlevel and/or engine oil temperature.

The method further comprises when EGR flow is not disabled due to theimpact of PCV flow hydrocarbons being below the threshold, disablingpurge and determining the impact of PCV flow hydrocarbons while purge isdisabled at a first frequency, the first frequency based on an engineoil temperature. Additionally, the method comprises after disabling EGRflow responsive to the impact of PCV flow hydrocarbons, disabling purgeand determining a subsequent impact of PCV flow hydrocarbons while purgeis disabled at a second frequency, the second frequency different thanthe first frequency. For example, the second frequency is a settime-based frequency and the first frequency is based on a set change inthe engine oil temperature, the second frequency higher than the firstfrequency such that purge is disabled more often at the secondfrequency.

The method further comprises re-enabling EGR flow responsive to theimpact of PCV flow hydrocarbons on the output of the intake oxygensensor decreasing below the threshold. In another example, the disablingEGR flow responsive to the impact of PCV hydrocarbons on the output ofthe intake oxygen sensor increasing above a threshold includes disablingEGR responsive to a diagnostic flag indicating degradation of anestimated fuel concentration in engine oil, the diagnostic flag set inresponse to an expected output of the intake oxygen sensor differingfrom an actual output of the intake oxygen sensor by a threshold amount,the expected output of the intake oxygen sensor based on an estimatedfuel evaporation rate from the engine oil. The estimated fuelevaporation rate is based on the output of the intake oxygen sensor, theestimated fuel concentration in engine oil, fuel composition, and engineoil temperature.

Disabling EGR flow includes disabling EGR during boosted engineoperation. Additionally, disabling EGR flow includes closing an EGRvalve positioned in a low-pressure EGR passage, the low-pressure EGRpassage positioned between an exhaust passage downstream of a turbineand an intake passage upstream of a compressor. The intake oxygen sensoris positioned downstream of an inlet of the low-pressure EGR passageinto the intake passage and the DPOV sensor is positioned in thelow-pressure EGR passage.

In another example, the disabling EGR flow described above may beresponsive to a degree of an impact of PCV flow hydrocarbons on theoutput of the intake oxygen sensor. The degree of impact of the PCV flowhydrocarbons may be based on the magnitude of the difference between theintake oxygen sensor output and the DPOV sensor output (if EGR isflowing) or the magnitude of difference between the intake oxygen sensoroutput and the expected blow-by (if EGR is not flowing). As themagnitude of one or more of these differences increases, the degree ofimpact of PCV flow hydrocarbons on the intake oxygen sensor mayincrease. The controller may then disable or not disable EGR based onthe degree of the impact of PCV flow hydrocarbons. For example, if thedegree of impact is greater than a threshold the controller may disableEGR. In another example, the controller may disable EGR for a longerduration and/or increase the impact of PCV flow checking frequency(e.g., second frequency described above) as the degree of the impactincreases.

As described above, HCs from PCV flow may impact the output of the IAO2and consequently influence the EGR flow estimate based on the IAO2output. HCs released into the intake passage via the PCV flow may resultfrom evaporation of fuel in engine oil in the engine crankcase. As theengine warms up, fuel may evaporate from the engine oil and be releasedas HCs into the PCV flow. These HCs may impact the IAO2 output duringboosted engine operation. Fuel in the engine oil may also affectadditional engine controls such as engine fueling. FIG. 5 shows a method500 for estimating a fuel concentration in engine oil and a fuelevaporation rate from the engine oil. Instructions for executing method500 may be stored in a controller (such as controller 12 shown in FIGS.1-2). Further, the controller may execute the method 500 as describedbelow.

At 502, the method includes determining an engine oil temperature (EOT).In one example, the EOT may be measured by a temperature sensorpositioned in the engine oil in the crankcase or estimated through amodel. At 504, the method includes determining a vapor pressure of thefuel based on the EOT and the type of fuel being used in the engine. Forexample, each type of fuel may have a constituent content with differentamount of heavy and light ends. In one example, the method at 504 mayutilize a vapor pressure model. The vapor pressure model may use thefuel constituent content (pre-determined based on fuel type and priorknowledge of fuel species that get accumulated in the oil) and themeasured EOT to determine the current fuel vapor pressure of thedominant constituents. At 506, the method includes obtaining an IAO2reading when both purge and EGR are disabled. The methods at 502 and 504may be performed concurrently with the method at 506. For example, thecontroller may obtain the IAO2 reading for estimating the fuelconcentration in engine oil only when purge and EGR flow are disabled.In another example, the controller may obtain the IAO2 reading forestimating the fuel concentration in engine oil (and subsequentlyadjusting engine operation based on the estimated fuel concentration inengine oil) in response to both purge and EGR being disabled. Asdescribed above, EGR flow being disabled may include when the EGR valve(e.g., LP EGR valve) is fully closed and no EGR is flowing into theintake passage upstream of the IAO2. Further, in another example, if EGRand/or purge are disabled for the fuel concentration and/or the PCVnoise estimation (described at FIG. 4), EGR and/or purge may not beenabled even if requested by another engine system during the estimationperiod.

At 508 the method includes determining the instantaneous concentrationof HCs in the engine oil by dividing the IAO2 output by the estimatedvapor pressure. The IAO2 output may be proportional to the concentrationof HCs in the gaseous phase while the determined concentration of HCs inthe engine oil is the concentration of HCs in the liquid phase. At 510the method includes determining the fuel evaporation rate from theengine oil based on a concentration gradient between the concentrationof HCs in the liquid phase (e.g., oil) and the gaseous phase (e.g.,air). In another embodiment, the fuel evaporation rate may be based onconsecutive estimates of the fuel concentration in engine oil.

At 512 the method includes storing the instantaneous concentration ofHCs in the oil (e.g., fuel concentration in engine oil) and the fuelevaporation rate in a memory of the controller. In one example, the fuelconcentration in engine oil and the fuel evaporation may be stored as afunction of EOT in a look-up table or chart. The engine controller maythen reference the stored look-up table or chart during subsequentcontrol routines wherein a fuel evaporation rate and/or fuelconcentration in the engine oil is required. At 514 the method includesobtaining IAO2 measurements at a set interval or frequency and thenupdating the stored concentration of HCs in the oil and fuel evaporationrate based on the new IAO2 measurements, as described at steps 502-510.The set interval for estimating and updating the fuel concentration inthe engine oil and fuel evaporation rate data may be based on the EOTand operational state of the engine. For example, if the engine iswarming up and the EOT is not at steady-state the interval forestimating may be shorter than if the EOT is at steady-state (e.g., notchanging substantially).

At 516 the method includes adjusting engine operation based on the fuelevaporation rate and the fuel concentration in the engine oil. In oneexample, adjusting engine operation may include adjusting fuel injectionbased on the fuel evaporation rate. For example, the controller mayreduce a fuel injection amount or pressure as the fuel evaporation rateincreases. In another example, the controller may adjust subsequent IAO2outputs based on the HC concentration in the oil. For example, the IAO2output may be corrected by the HC concentration in the oil such that thecorrected IAO2 output reflects a decrease in intake oxygen due to EGRonly and not due to PCV HCs. As a result, the controller may estimateEGR flow (e.g., LP EGR flow) based the adjusted IAO2 output. Thecontroller may then adjust EGR flow (e.g., adjust a LP EGR valve) basedon the estimated EGR flow. In alternate examples, the controller mayalso adjust HP EGR flow based on the adjusted IAO2 output in order toadjust a total amount of EGR provided to the engine. In some examples,the fuel evaporation rate may be used to estimate and/or predictsubsequent IAO2 outputs. If an actual IAO2 differs by a threshold amountfrom a predicted IAO2 output, degradation of the fuel evaporation ratemay be indicated. If the accuracy of the fuel evaporation rateestimation is degraded (e.g., reduced), EGR flow estimates based on thefuel concentration in the oil may be inaccurate. As a result, thecontroller may set a flag indicating that the change in intake oxygenmeasured at the IAO2 due to PCV HCs may not be compensated for with themethod outlined at FIG. 5. As a result, the controller may disable EGRflow for a duration until the impact of HCs at the IAO2 is reduced, asdescribed above with reference to FIGS. 4A-4B (at step 420). In yetanother example, if the fuel evaporation rate exceeds a threshold rate,the controller may set a flag as an indicator to the EGR arbitrationstrategy shown at step 420 in FIG. 4A. Thus, the method shown at FIGS.4A-4B may include disabling EGR flow for a duration based on theestimated evaporation rate increasing above the threshold rate. Inalternate examples, the fuel evaporation rate may be used to adjustadditional engine controls such as fuel injection routines or adjustingestimates of engine oil viscosity for additional control routines suchas oil minder.

As one embodiment, a method for an engine comprises adjusting engineoperation based on a fuel concentration in engine oil, the fuelconcentration based on an output of an intake oxygen sensor when purgeand EGR flow are disabled, engine oil temperature, and fuel composition.The method further comprises estimating a fuel evaporation rate from theengine oil based on a concentration gradient between the fuelconcentration in engine oil and the output of the intake oxygen sensor,the output of the intake oxygen sensor indicative of a fuelconcentration in intake air. In one example, adjusting engine operationincludes adjusting fuel injection to the engine based on estimated fuelevaporation rate, an amount of fuel injected decreasing with increasingestimated fuel evaporation rate. In another example, adjusting engineoperation includes disabling EGR flow for a duration when an actualoutput of the intake oxygen sensor differs from an expected output ofthe intake oxygen sensor by a threshold amount, the expected outputbased on the estimated fuel evaporation rate. In yet another example,adjusting engine operation includes adjusting a position of an EGR valvebased on the output of the intake oxygen sensor relative to the fuelconcentration in engine oil. The EGR valve may be a low-pressure EGRvalve in a low-pressure EGR system. In another example, the EGR valvemay be a high-pressure EGR valve in a high-pressure EGR system.

The fuel concentration may be further based on crankcase pressure andboost conditions. For example, the fuel concentration may only bedetermined when the engine is boosted. The intake oxygen sensor ispositioned in an intake passage downstream of an inlet of a low-pressureEGR passage into the intake passage, the low-pressure EGR passagepositioned between an exhaust passage downstream of a turbine and anintake passage upstream of a compressor.

As another embodiment, a method for an engine comprises during boostedengine operation, flowing PCV gases to an engine intake upstream of anintake oxygen sensor; estimating a vapor pressure based on an engine oiltemperature and a composition of fuel; estimating a fuel concentrationin engine oil based on the estimated vapor pressure and an output of theintake oxygen sensor when purge flow and EGR are disabled; and adjustingan EGR valve based on the estimated fuel concentration in engine oil andthe output of the intake oxygen sensor. The method further comprisesestimating a fuel evaporation rate from the engine oil based on aconcentration gradient between the output of the intake oxygen sensorand the estimated fuel concentration in engine oil. Additionally, themethod comprises adjusting engine fueling based on the estimated fuelevaporation rate.

Further still, the method comprises setting a diagnostic flag to disableEGR and indicating degradation of the estimated fuel concentration inengine oil due to an expected output of the intake oxygen sensordiffering from an actual output of the intake oxygen sensor by athreshold amount, the expected output of the intake oxygen sensor basedon the estimated fuel evaporation rate. After setting the diagnosticflag to disable EGR, the method may include removing the diagnostic flagto re-enable EGR when the expected output of the intake oxygen sensorbased on the estimated fuel evaporation rate is within the thresholdamount of the actual output of the intake oxygen sensor. In one example,the method includes disabling purge at a first frequency in order todetermine if degradation of the estimated fuel concentration in engineoil is indicated, the first frequency based on engine oil temperaturewhen EGR is not disabled due to an impact of hydrocarbons on the outputof the intake oxygen sensor. In another example, the method includesdisabling purge at a second frequency, higher than the first frequency,in order to determine if degradation of the estimated fuel concentrationin engine oil is indicated, the second frequency based on a set timeduration when EGR has been disabled due to the impact of hydrocarbons onthe output of the intake oxygen sensor.

Additionally, the method comprises storing the estimated fuelevaporation rate and the estimated fuel concentration in engine oil as afunction of engine oil temperature in a memory of a controller of theengine. A controller of the engine may obtain an output of the intakeoxygen sensor at a set interval when purge and EGR are disabled and thenupdate the stored fuel evaporation rate and fuel concentration in engineoil, the set interval based on engine oil temperature. Duringnon-boosted engine operation, the method includes flowing PCV gases tothe engine intake downstream of the intake oxygen sensor and adjustingthe EGR valve based on the output of the intake oxygen sensor on notbased on the estimated fuel concentration in engine oil.

Turning now to FIG. 6, a graphical example of adjustments to EGR flowbased on estimates of the impact of PCV HCs on an IAO2 output is shown.Specifically, graph 600 shows changes in engine oil temperature (EOT) atplot 602, changes in a purge off command (e.g., command to disablepurge) at plot 604, changes in EGR flow (e.g., LP EGR) at plot 606,changes in boost at plot 608, changes in a difference between an IAO2output and DPOV sensor output at plot 610, changes in a differencebetween an IAO2 output and expected blow-by at plot 612, and changes toa set diagnostic flag based on the fuel evaporation rate at plot 614. Asdiscussed above, the flag based on the fuel evaporation rate mayindicate the impact of PCV HCs on the IAO2 output is over a threshold.

Prior to time t1, the engine is boosted (plot 608) and the EOT may beincreasing from a lower threshold temperature (plot 602), therebyindicating the engine oil is warming up. As a result, the controller maydisable purge flow (or command purge flow off) at a first frequency, ΔF1(plot 604). Disabling purge flow may include closing a canister purgevalve to stop the flow of purge gases to the engine intake. If the purgevalve is already closed, the controller may maintain the valve in theclosed position during the command to disable purge. The first frequencyΔF1 may be based on the EOT such that purge is commanded off todetermine the PCV noise on the IAO2 for every set increase in EOT. Forexample, the set increase may be 5° C. such that purge is disabled toperform the PCV noise check (e.g., impact of PCV HCs on the IAO2 output)every increase in EOT by 5° C. In alternate examples, the set increasein EOT may be more or less than 5° C. Also prior to time t1, EGR may beenabled (e.g., LP-EGR valve at least partially open and LP-EGR isflowing). After disabling purge, the controller may re-enable purge.However, if purge is commanded closed based on additional engineoperating conditions, the purge valve may remain closed even if purgeflow is not disabled for the PCV noise estimating routine.

At time t1, the difference between the output of the IAO2 sensor and theoutput of the DPOV sensor may be greater than a first threshold, T1(plot 610). Since EGR is flowing, both the IAO2 output and the DPOVsensor output may provide estimates of EGR flow. If these estimatesdiffer by an amount greater than the first threshold T1, blow-byhydrocarbons from PCV flow may be affecting the IAO2 sensor output. Inresponse to the difference between the output of the IAO2 and the outputof the DPOV sensor being greater than the first threshold T1, thecontroller may disable EGR (plot 606). For example, the controller mayclose a LP EGR valve positioned in a LP EGR passage in order to stop LPEGR flow from flowing into the intake passage upstream of the IAO2sensor.

After disabling EGR flow at time t1, the controller may re-check the PCVnoise at the IAO2 by disabling purge and re-checking the differencebetween the IAO2 output and predicted blow-by at a second frequency ΔF2.The second frequency ΔF2 may be based on set time intervals rather thanbased on EOT. In some examples, as shown in FIG. 6, the second frequencyΔF2 may be higher than the first frequency ΔF1 such that the PCV noiseimpact on the IAO2 is checked more frequently after purge has beendisabled due to PCV noise being above a threshold. In alternateembodiments, the first frequency and the second frequency may besubstantially the same.

Between time t1 and time t2, a flag may be set based on the estimatedfuel evaporation rate (plot 614). As discussed above, if the impact ofPC HCs on the IAO2 output may not be compensated for using an estimatedfuel concentration in the engine oil, the controller may disabled purge.For example, if the IAO2 is different than predicted by the fuelevaporation rate by a threshold amount, the controller may set the flagresulting in disabling EGR. Since EGR is already disabled between timet1 and time t2, the EGR remains off responsive to the flag.

At time t2, the difference between the IAO2 output and the expectedblow-by decreases back below a second threshold T2 (plot 612), therebyindicating the impact of PCV noise on the IAO2 has decreased back belowa set threshold. As a result, the controller may re-enable EGRresponsive to the difference between the IAO2 output and the expectedblow-by being below the second threshold T2. Re-enabling EGR flow mayinclude opening the LP EGR valve and adjusting LP EGR flow to arequested level. Additionally, the second threshold T2 may be differentthan the first threshold T1.

At time t3 the EOT reaches steady-state such that the EOT issubstantially steady and no longer increasing (plot 602). As a result,since EGR is enabled, the controller may only disable purge and checkthe impact of PCV hydrocarbons on the IAO2 once while the EOT remains atsteady-state conditions. In alternate embodiments, the controller maycheck PCV noise and disable purge more than once, but at a frequencylower than the first frequency ΔF1 and the second frequency ΔF2.

At time t4 the EOT begins increasing again above the steady-state level(plot 602). As a result, the controller begins disabling purge andchecking PCV noise at the IAO2 at the first frequency ΔF1. At time t5,the controller determines that the difference between the IAO2 outputand the expected blow-by (BB) is greater than the second threshold T2.In response to the difference between the IAO2 output and the expectedBB being greater than the second threshold T2, the controller commandsEGR flow off (e.g., closes the LP EGR valve). However, since EGR flow isalready disabled (plot 606), the controller maintains the disabled EGRflow at time t5. After time t5, the controller begins disabling purgeand checking the PCV noise at the IAO2 at the second frequency ΔF2.

As shown at time t1 in FIG. 6, during a first condition when EGR isflowing and purge is disabled, an engine controller may disable EGR whena difference between an output of an intake oxygen sensor and an outputof a DPOV sensor is greater than a first threshold T1. As shown at timet5, during a second condition when EGR is not flowing and purge isdisabled, the engine controller may disable EGR flow when a differencebetween the output of the intake oxygen sensor and an expected blow-byflow is greater than a second threshold T2. Disabling EGR flow duringthe second condition may include maintaining EGR flow off (e.g.,maintain the EGR valve closed) until the difference between the intakeoxygen sensor output and the expected blow-by decrease back below thesecond threshold T2. The controller may then turn on EGR if EGR isrequested based on additional engine operating conditions.

As shown at time t2, the controller may re-enable EGR flow after thedisabling EGR when the difference between the output of the intakeoxygen sensor and the expected blow-by flow is not greater than thesecond threshold T2 when purge is disabled. As discussed above theexpected blow-by may be stored in a memory of a controller in a look-uptable as a function of current engine speed and manifold pressure.

As shown prior to time t1 and between time t4 and time t5, when engineoil temperature is not at steady-state, the controller may disable purgeand determine the difference between the output of the intake oxygensensor and the output of the DPOV sensor or the difference between theoutput of the intake oxygen sensor and the expected blow-by flow at afirst frequency. Then, as shown between time t3 and time t4 when theengine oil temperature is at steady-state, the controller may disablepurge and determine the difference between the output of the intakeoxygen sensor and the output of the DPOV sensor or the differencebetween the output of the intake oxygen sensor and the expected blow-byflow only once.

As shown between time t1 and time t2 and after time t5, after disablingEGR, the controller may disable purge and determine the differencebetween the output of the intake oxygen sensor and expected blow-by flowat a second frequency, the second frequency higher than the firstfrequency. As discussed above, the DPOV sensor is positioned in alow-pressure EGR passage and the intake oxygen sensor is positioned inan intake passage downstream from a PCV passage inlet during boostedconditions and downstream from an inlet of the low-pressure EGR passage.

In this way, when hydrocarbons from PCV flow are impacting the output ofan intake oxygen sensor, an engine controller may temporarily disableEGR flow. Then, when the impact of PCV flow hydrocarbons reduces below athreshold, the controller may re-enable EGR flow. The controller maythen estimate EGR flow based on the output of the intake oxygen sensor.In one example, the output of the intake oxygen sensor may be adjustedbased on an estimated fuel concentration in engine oil. As such, atechnical effect is achieved by either adjusting an intake oxygen sensoroutput to compensate for PCV hydrocarbons or temporarily disabling EGRflow when the effect of PCV hydrocarbons on the intake oxygen sensor isabove a threshold. In this way, EGR flow adjustments may only be madewhen the EGR flow is estimated based on an intake oxygen sensor outputreflective of a decrease in intake oxygen due to EGR only and not due toPCV flow. As a result, EGR system control may increase and engineemissions may be maintained at desired levels.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory. The specific routinesdescribed herein may represent one or more of any number of processingstrategies such as event-driven, interrupt-driven, multi-tasking,multi-threading, and the like. As such, various actions, operations,and/or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedactions, operations and/or functions may be repeatedly performeddepending on the particular strategy being used. Further, the describedactions, operations and/or functions may graphically represent code tobe programmed into non-transitory memory of the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method for an engine, comprising: during engine oil warm-up,operating with EGR while purging fuel vapors to an engine intake withpurge flow disabled at a first frequency; and in response to adifference between EGR estimated by an oxygen sensor and EGR estimatedby a pressure sensor being higher than a threshold, disabling the purgeflow at a second, higher frequency.
 2. The method of claim 1, whereinthe EGR estimated by the oxygen sensor includes EGR flow rate estimatedvia an intake oxygen sensor positioned upstream of an intake throttleand downstream of a charge air cooler, and wherein the EGR estimated bythe pressure sensor includes EGR flow rate estimated via a differentialpressure over valve sensor coupled across an EGR valve.
 3. The method ofclaim 2, further comprising, in response to the difference being higherthan the threshold, disabling EGR.
 4. The method of claim 3, furthercomprising, while operating with EGR, checking PCV noise on the intakeoxygen sensor when the purge flow is disabled based on an output of theintake oxygen sensor relative to an output of the differential pressureover valve sensor.
 5. The method of claim 4, further comprising, afterdisabling EGR, checking PCV noise on the intake oxygen sensor when thepurge flow is disabled based on the output of the intake oxygen sensorrelative to predicted blow-by.
 6. The method of claim 1, wherein thefirst frequency of disabling purge flow is based on engine oiltemperature, and wherein the second frequency of disabling purge flow isnot based on engine oil temperature.
 7. The method of claim 6, whereindisabling purge flow at the first frequency based on engine oiltemperature includes closing a canister purge valve for every thresholdincrease in engine oil temperature.
 8. The method of claim 6, whereinthe second frequency of disabling purge flow is based on a set timeduration.
 9. A method for an engine, comprising: flowing EGR from anengine exhaust to an engine intake via an EGR valve; commanding canisterpurge flow off at a first frequency; determining PCV noise on an intakeoxygen sensor while the canister purge flow is off; and in response toincreased PCV noise, disabling EGR and commanding canister purge flowoff at a second, higher frequency.
 10. The method of claim 9, whereindetermining PCV noise on the intake oxygen sensor includes comparing EGRflow estimated by the intake oxygen sensor with EGR flow estimated by adifferential pressure over valve sensor coupled to the EGR valve. 11.The method of claim 10, further comprising indicating increased PCVnoise in response to a difference between the EGR flow estimated by theintake oxygen sensor and the EGR flow estimated by the differentialpressure over valve sensor being higher than a threshold.
 12. The methodof claim 10, further comprising, determining PCV noise while EGR isdisabled by comparing the EGR flow estimated by the intake oxygen sensorwith an expected blow-by amount, the expected blow-by amount based onmanifold pressure and engine speed.
 13. The method of claim 9, whereinthe EGR is one of high pressure and low pressure EGR.